Feeding of magnetic sheet material



1953 A. FOWLER FEEDING 0E MAGNETIC SHEET MATERIAL 4 Sheets-Sheet 1 FiledMay 16. 1951 INVENTOR. 14L EXANDI? 1 01 1 45? BY Z z ATTOEA EYJ 174 vfAlDec. 1, 1953 Filed May 16. 1951 A. FOWLER FEEDING OF MAGNETIC SHEETMATERIAL L/NE 1 LINE 2 ONE REVOLUTIONF CLUTCH 4 Sheets-Sheet 2 INVENTOR.ALEXANDER FOWLEQ ATTQQA/EYS Dec. 1, 1953 FOWLER 2,661,208

FEEDING OF MAGNETIC SHEET MATERIAL Filed May 16. 1951 4 Sheets-Sheet 3LINE 1 L/NE 2 IN V EN TOR. flLEX/M/DE/Z FOWLER Dec. 1, 1953 A. FOWLER2,661,208

FEEDING OF MAGNETIC SHEET MATERIAL Filed May 16. 1951 4 Sheets-Sheet 442 IN V EN TOR.

380 Al E'XANDER FOWLER Patentecl Dec. 1, 1953 UNITED STATES PATENTOFFICE FEEDING'OF MAGNETIC SHEET MATERIAL Alexander Fowler, Brooklyn, N.Y., assignor to Hercules Electric & Mfg; a., Inc., Brooklyn, N. Y., acorporation of New York Application May 16; 1951, Serial No. 226,656

28 Claims. 1

This invention relates to the feeding of sheet material, and moreparticularly to the automatic separation and feeding of single sheets insuccession from a stack of ferromagnetic sheets.

The primary object of the present invention is to generally improvemagnetic sheet separation and feeding apparatus. A more particularobject is to produce a wide separation of the sheets magnetically.

A further object of the invention is to guard against the possibility ofmore than one sheet adhering to the feed roller. In accordance with myinvention thisobject of insuring the feeding ofonly a single sheet at atime may be fulfilled by energizing the main induction coil with aslowly growing current (or one tooth of a low speed saw-tooth wave). Insuch case the topmost sheet begins to separate ahead of the nextsubjacent sheet, and so on, and there is a relatively wide andindividual separation of the sheets as the topmost sheet reaches thefeed roller. When the top most sheet reaches the feed roller theenergization of the main induction coil is terminated, and the topmostsheet is promptly fed from the stack.

A further object of the present invention is to eliminate the need foran elevator table by affording so substantial a lift of the topmostsheet as to accommodate the reduced height of the stack as it isconsumed.

Still another object of the present invention is-to provide electroniccircuits and apparatus for supplying the desired saw-tooth or growthcurrent for energization of the magnetic field. The term growth currentis more apt than sawtooth current because for the present purpose theimportant thing is that the current grow from a relatively low value toa relatively high value, but there is no need for the increase to be alinear one.

Still another object of the present invention is to provide electroniccircuits which will operate on a single phase power supply, and on athree phase power supply.

In many cases the sheets of the stack tend to adhere tightly because ofan oil film thereb'=- tween. This is particularly true in winter, foralthough the separating means may be located in a building, the sheetsare more usually stored outdoors or. inan unheated storage shed fromwhich they are brought to the separating means without a long warmmpperiod in which they might gradually acquire the building temperature;Further objects or the present invention are to provide apparatuswhichwill help overcome adhesion between the sheets, and which.

will prevent repeated or renewed adhesion of the sheets while in thesheet separating apparatus.

For certain purposes it may be desired to feed.

sheet, and a further feature and object of the present invention is toprovide means for this purpose.

To accomplish the foregoing generalobjects, and. other more particularobjects which. will hereinafter appear, my invention resides in thesheet separating and feeding elements, and their relation one toanother, as are hereinafter more particularly described in the followingspecification. The specification is accompanied by drawings in which:

Fig. 1 is a plan view of sheet separating and feeding apparatusembodying features of my invention;

Fig. 2 is a section taken in elevation approximately in the plane of theline 2-4! of Fig. 1;

Fig. 3 is a schematic wiring diagram explanatory of one form of myinvention;

Fig. 4 is explanatory of a current growth curve or saw-tooth wave usedin my invention;

Fig. 5 is explanatory of the operation of a modified electronicapparatus shown in Fig. 7

Fig. 6 is. a current growth curve generally similar to that shown inFig. 4 but explanatory of a modification;

Fig; '7 is a schematic wiring diagram for an electronic form of myapparatus energized from asingle phase power supply; and

Fig; 8 is a schematic wiring diagram of electronic apparatus energizedfrom a three. phase power supply.

The present application is a continuation-inpart of my prior applicationof like title, Serial No. 129,662, filed November 26, 1949, and some ofthe foregoing objects, as well as the subject matter of Figs. 1 through4 hereinafter described,

have been tak n from that application, while paratus further includesfeed means generally designated 2E3 for feeding the uppermost sheet 21';through the coil it and away from the stack 54. The feed means 25preferably includes an electro-magnetic roller 24 capable of feedingsheet 22 with the latter disposed beneath the roller. The roller ispreferably intermittently driven, as by means of a magnetic clutch 2%disposed between the roller and a constantly rotat ing motor 28. Thelatter may rotate one or more sets of later feed rollers, indicatedschematically at 25, through a drive 21.

The sheets may be stacked between guide plates 30, supported within sideplates 32, preferably by means of adjusting screws 32, so that sheets ofdifferent width may be accommodated. The sheets are aligned at theirforward edge by means of front stops such as the posts 35, which arepreferably made of non-magnetic material. The table 12, on the otherhand, may be made of ferrous or magnetic material in order to repel andraise even the last sheet of the stack.

Before referring to the wiring diagram, attention is directed to theslip rings 33 (Fig. l) and brushes ta which supply magnetizing currentto the coils 42 of the feed roller Also the feeler M (Fig. 2)controlling switch contacts i When the topmost sheet 22 reaches the feedroller 2d the feeler is moved from a lower down-position to the positiont4 shown, thus closing the normally open contacts at. It will beunderstood that the showing in Fig. 2 is merely schematic, and that inpractice a fully enclosed and sensitive microswitch may be used for theintended purpose. Moreover, other means to discriminate be-- tween theabsence or presence of a sheet may be used.

It is desirable to delay re-energization of the main induction coiluntil the trailing edge of a preceding sheet has safely left themagnetic feed roller 2 1. This avoids any possibility of the next topsheet being caused to fly upward prematureh in which case the forwardportion of said sheet may strike the bottom of the trailing portion ofthe preceding sheet, thus holding it back both physically andmagnetically, or, in the alternative, causing the second sheet to beprematurely pulled forward by the first sheet. i'his result may beaccomplished by using a time delay relay, or by using a second feeler,and the latter ar rangement is schematically shown in Fig. 2 in which itwill be seen that a second feeler is provided outside the stack, saidfeeler serving to close contacts Ell when engaged by a sheet passingthrough feed rollers 25. This is described further as an incident to thedescription of Fig. 3 which follows.

Mo'tm' driven growth curve circuit Referring now to Fig. 3, the mainfeature of this arrangement is that the induction coil it is energizedby a gradually increasing current which starts at zero and rises to adesired value. Thus the current may follow an intermittent saw-toothwave such as that illustrated in Fig. 4. In Fig. 4 it will be seen thatthe current rises from the point 5% to a maximum at 5B, whereupon it iscut off and remains off until the point 58. The interval between points56 and 5t corresponds to the time during which the sheet is away fromthe stack by the feed roller. When i main induction coil it is reenerglzed beginning at point 5%. the current again increases to amaximum as indicated at lit and is again out If the induction coil isenergized in this manner the topmost sheet tends to be raised from thenext subjacent sheet before the latter is raised at all, whereupon bothrise before the third sheet rises, so that the fanning out or divergenceor separation of the sheets is maintained as the induction coil isfurther energized. In any event the topmost sheet alone reaches the feedroller, and the induction coil may then be deenergized without danger ofthe feed roller holding more than one sheet. Indeed, by promptlytie-energizing the induction coil when the topmost sheet reaches thefeed roller it is found that the feed roller may be left at fullenergize.- tion, and further that it may be kept under constantrotation. Thus the apparatus of Fig. 3 is more complicated inintroducing suitable means to apply a growth current or saw-toothcurrent to the induction coil, but may be simplified in other respectsas by eliminating the electrically operated clutch for the feed rollershown in Fig. 1.

Referring to Fig. 3, a main power switch 62 is closed to supply powerfrom an ordinary source indicated by lines I and 2. This supplies powerthrough conductors t3 and it to feed roller 24, the return being throughconductors i and 16 to line 2. The power supply to the induction coil Itis varied by of suitable variable impedancc 8t. If the power supply isalternating current this be either a conventional Varies or a rheostat.Variac a trade name of the General Radio Company for a variable voltage(disclosed in Patent #2,6G9,013). It a device which increases ordecreases voltage by mechanical rotation of a contact engaging thewindings of a transformer. If the power supply is direct current thevariable impedance would, of course, be a rheostat. The power to the'Variac fill is from line i through conductors 68, "H2 and iii, thereturn being through conductors 84, it, and 76, and back to line 2.

The Variac is driven through a one-revolution clutch and reductiongearing Bl by means of a motor at energized from the power line throughconductors 9i) and E52. One-revolution clutch 81 is electricallyoperated, and is initially engaged because of a supply of power fromline I through conductor Qt, normally closed contacts 96 of relay and aconductor lull. The return is through a conductor It? to line 2. Theresulting rotation of the Variac causes a growth in output current fromzero until the one-revolution clutch disengages. The power available inthis way for the main induction cell It could grow to a value greaterthan needed to raise the first sheet into engagement with the feedroller, but the power supply is interrupted by suitable means as soon asthe sheet reaches the feed roller. The mechanical rotation of the Variacis continued under drive of motor 88, and is terminated after onerevolution by the operation of the one-revolution clutch, thus preparingthe apparatus for the separation and delivery of the next sheet.

In the meantime the growing current is supplied frcm the Variac throughconductor Hi l, the normally closed contacts Hit of relay and conductorHi8 to the induction coil id, the return being through conductor i i Inthe present apparatus the complete passage of a sheet is determined bythe use of two feelers as shown in Fig. 2, instead of a single feelercombined with a time delay relay, although either arrangement might beused. The first and second feelers or microswitches are inace 1,2108:

dice-ted at. 4,4 and 48'. The contacts are normally open. When. thetopmost sheet flies upward and reaches the feed roller it closes, theswitch 44, thus energizing. relay coil H2 and so opening the contactsI06 and thereby interrupts.

ing the energization of the induction coil. This;

drops all sheets but the uppermost. sheet, the latter being. held by thefully magnetized. feed roller, which may be constantly rotated and whichprommptly begins. feeding the sheetout of the stack. In this case thefeed roller may be permanently magnetized, as by making thesame ofAlnico. or other highly magnetic material. However, as here shown itismagnetized electrically, with a constant current supply.

Energization of relay 93. opensthe contacts 98 and thus de-energizes theelectrically controlled.

clutch 86 so that when itdisengages at the end of a single revolution itwill not again engage unless and until the preceding sheet has been fedentirely out of the apparatus.

When the trailing edge of the sheet leaves the feeler 44 the relay coilI I2 is not yet de-energized because of the action of the feeler 48, andtherefore the main induction coil is not yet re-energized. However, whenthe trailing edge of the sheet leaves the second feeler t8 the relaycoil H2 is de-energized, the contacts 96 and 1&6 are again closed, andthe induction coil is again energized to raise another sheet to the feedroller.

In Fig. 3 the drive motor for feed roller 24 is not shown. It maybe anymotor connected to the available power. supply. It may run continuously,and the feed roller may be energized continuosly, with no disadvantageexcept a slight waste of electric power. Continuous feed of sheets oneafter another is contemplated. However, by additions to the circuit onemay provide intermittentv energization of the motor or/and the roller,and manual or treadle controlled feed. Thus a clutch '26 is shown inFig. 1, for intermittent operation of the feed roller while permittingcontinuous run of the motor 28. of these features are described later.

It will be seen that the described apparatus provides a graduallyincreasing current in the main winding It. The term gradually is to beunderstood in a relative sense, for if the apparatus is operated at highspeed to feed a sheet every few seconds the entire growth of the currentmay occur in a very short time, yet that time is long compared to aninstantaneous-application of full current. With a growth current thefirst sheet will be raised from the second, following which the secondwill be raised from the third, while the first will. tend to maintainits distance from the second, and so on, thus causing all the sheets toseparate from one another and to fan out over asubstantial distance.This eliminates the need for critical adjustment of the circuit elementsand current values. It provides a large tolerance in the. operation ofthe apparatus, so that if one sheet varies somewhat from another inthickness or weight, etc., the operation will nevertheless beunhampered.

Even the refinement of an elevator table has been found unnecessary, andin a particularcase I have located the feed roller 16" above the table,making it possible to feed sheets from a stack 14;" high. The stack maybe fed down to a thickness of, say 2", so that in effect, a 12" stackmay be fed, and then another 12" stack added to the residual sheets.

The: residual stack is preferably left on the table because it acts as apriming stack and Some Single phase electronic circuit The system ofFig. 3 is an electro -mechanical system because of the motor driveemployed to. produce the growth current. However, a substantially whollyelectronic system is shown in.

Fig. "l, and eliminates the need for the motor,

clutch, and Variac shown in Fig. 3'. The specific,

system employs a thyratron, and firesthe thyratron by means of a triggerwave. The main induction coil of the apparatus receives the D. C. orrectification increments. The trigger wave isshifted, and this providesa growth current because of the increasing increments of plate currentas the firing point of the thyratron changes.

The plate and grid waves of the thyratron may be of like frequency andeach of uniform magnitude, but relatively shiftable in phase, With thewaves out of phase no current will fiow, and

with the waves in phase a maximum current will flow. At intermediatevalues the current. supplied by the thyratron may be varied by shiftingthe phase of the trigger wave supplied to the grid. On the other handthe trigger wave and the plate wave may be given. a phase differencewhich is maintained constant, and the axis of the trigger wave may beraised or lowered by chang ing the magnitude of a bias superimposedthereon. This also has the effect of varying the plate current, andbecause either method or a com bination or both may be employed I preferto use the broad term shift in respect to the trigger wave, in order toinclude either a phaseshift or a bias shift, or both.

Referring to Fig. 7, the main coil is shown, at it, and the magneticfeed roller at 24, the latter being driven by a motor 28. Single phasepower is supplied at lines I and 2. The apparatus of Figs. 1 and 2applies to this circuit, except that the clutch 25 of Fig. 1, and thesecond trip switch, or microswitch 48 of Fig. 2, are omitted. The. firsttrip switch it is employed.

When the main switch I It is thrown on, the

transformer l I 2 is energized, heating the filament of thyratron tubeti l, through secondary 6..

After the tube is warmed up a circuit breaker, l 1.8

is closed, and then the operating switch I20 is closed, which starts thecycle as follows:

Relay I22 is energized from line i through the normally closed contactsof relay 535, which s still ale-energized because the trip switch 54 isopen. Actuation of relay iii-2 opens the com tacts I28. When contacts12s of relay 22 open.

the growth current starts and the sheets begin to separate. The growthcurrent is obtained from the transformer secondary int, and iscontrolled by thyratrcn H 3. A trigger wave is su plied from transformersecondary its to the grid;

The resistor I32 and capacitor ltd provide a phase shifting circuit forthe trigger wave. The series resistor it limits the grid current.Resistor I32 of the phase shifting circuit is val-is able to permit linecontrol of the phase relation of trigger wave or grid voltage to platevoltage. sired the manual operation explained latter.

Secondary its of transformer t in con- To summarise, in the special casewhere time junction with full-wave rectifier Hill and potendelayde-energization is wanted, in addition to tiometer I42, provides apositive D. C. grid pcmagnetization, the thyratron serves tential orbias which raises the axis of the tin purposes in one, and istrouble-free in wave and so increases the amount or plate cur--maintenance. rent fed through the main sheet separatin coillilnergization of relay opens contacts I24, I6. This bias may set forthe lnaxirnt dedeenergizing relay and permitting contacts sired amountof thyratron plate current. T ans- 1238 to again close. This bucks thetrigger Wave former secondary and rectifier supply a 10 elevatingpotential of thyratron lit, and so colnegative bias to lower the or thetrigger lapses (either completely or partially) the field wave. Thethyratrcn plate current is in alter in the main coil It. The field inthe main coil hate or positive half waves, as suggested is collapsedbecause the trigger Wave axis is low- 5. The trigger wave from secondarytoi has ered by rectifier supply Mil, M8, thus pulling its phasedisplaced by the resistor and capac the A. C. trigger wave down to thepoint Where itor I32, Ital, and has its horizontal axis raised thethyratron does not fire (01' tires at desired by the bias supply its,the amount being minimum),

adjustably controlled by potentiometer no At the same time relay I alsocloses its conthe circuit goes into operation, however, the cl tacts andi s. Contacts ItZ initiate the cycle feet of the rectifier circuit Mt,its is to pull the so of the upper thyratron tu'oe ill? with the aidaxis of the wave down again. it is initi of secondaries and tilt; oftransformer ITO. pulled down to a point where none, or i' Secondary -aesthe trigger wave, and sired, only a small chip or plate curl I apacitorIlt provide phase as shown at in 5. The amount wave, which controls theis pulled down then. decreases by reason. ratron and so controls theole- R. C. decay circuit Hi2, 7). of the A. C, grid voltage Wave risefiring of the thyratron keeps rncvi to the left, thus causing larger ofplate current to flow through as shown at I56 and IE8 in Fig. eter I60(Fig. '7) is an additional or 8: 25 oi" the gh rectifier Hit and po- '1relay contacts 562 leadand resistors Hit, i238, potential to thyratronwhatever plate current is aeitor .W, its, thereby trol which may or maynot he is a. required to ener ize the magnetic roller at its particularapplication. It controls how lower stage of magnetization. A. C. Wave isbrought down. 3') Contacts i" itiate operation of a time .4 around tuheI94. Tuhe I554 a decay circuit to act as a timer .-,y rotation of thefeed roller after the the roller (as indicated by of the trip switch 2The time delay mplished through grid rectification by or resistor E96and capacitor E98. The resistor 2% is used to limit grid current.

Because of grid root ation the capacitor ap- 45 pl a negative potentialon the grid of the tube, and plate current does not flow. However, whenthe contacts Wt close the charge stored in capacitor dur 1g tie gridrectification period the discharges through the grid circuit 52222, andwhen the d charge has reached a certain point the tube wi It is thistime required for that results in the desired time delay action of thecircuit.

When the tube i relay 9 is energized, cl .2; contact- 1 and Contacts 264inin the sense that if there is 1So With, then less drop would be neeJe.a certain plate current value. In a s fore the duplicate controls maynot he 11 eded, and in a simpler circuit one the other may be employedalone.

Leaving the lower part or the diagram produces the growth current, theone of the main coil It causes the sheet to it reaches the rol r andswitch a l, closing the latter relay IEE, which functions to rnagnetxzeroller 24 and to start the motor 533. particular circuit here own the nof the feed roller thyratron tuhe it? controlled r "c two widelydifferent or u.

of magnetization of the l. roll, as Ve-ll crease the throo h magneticroller 24 complete cut-off when the feed roll not in by supplying morepotential than preuse. A relatively small magn t 1 :iously ap; iedthrough contacts 462 of relay I25 to the grid of thyratrcn For thispurpose the on 15 cent .ctentiometer 208 is made higher than that of potometer i822, At the oa..'l th closing of clay contacts 2555 enert feedmotor to through switch 2 iii, rectifier It, and 2m.

so far described the operation would be wholly automatic, he delivery ofone sheet follo ing another, but in many applications a or p al.control. is Wanted, and for this purpose it is merely necessary to addany convenient form. lanual or pedal switch 22a in quate to hold thetoprnos' shoot while the coil I 6 is being tie-energized to per t do ofthe othe* sheets. A d gree of magnetization employed to actu feed thesheet.

It may be explained that it find it to employ a thyratron as switchdifficulty with oxidation or contac' of ordi mechanical relays. Thethyratron far '1 as an energy controlling thus el ing the need for apower rheostat with dissipation of energy to bring the feed down todesired cnergization. .oreover, we r incorporate in the tuhe circuitswitch 220 13F" lly open switch. Thus to provide a time delay actionbefore vy or the diagr. shows two arrangements in one, for the magneticroller current, which delay dewith automatic operation switch 2H) wouldbe .486. or omitted, and the closed and there would be no manual or foottreadle switch, but with switch 2I0 open it becomes necessary for anoperator to close a manual or foot treadle switch 220 to initiate theoperation. The motor is a shunt motor symbolized at 28. but electricallythe terminals 2I6 represent the connections to the field of the motor,while the terminals we represent the connections to the armature of themotor. A shunt motor is used in order to give a wide range of speedcontrol, and also because it can be started and stopped more readilythan a single phase induction motor.

When the sheet leaves the feed roller 24 the trip switch 44 opens andrelay I 26 is de-energized. This opens contacts I62 and I64, and permitsclosing of contacts I24. The opening of contacts I6 cuts off the currentflow through tube I94, deenergizing relay H32, and opening contacts 204and 206. The opening 0? contacts 206 stops the motor. The opening ofcontacts 204, in conjunction with the opening of contacts I62 of relayI26, completely tie-energizes the roller after elapse of a time intervalcaused by the delay circuit I84, I86 and [88. The closing of contactsI24 operates relay I22, thereby opening contacts I28, and so againinitiating the growth current in the main sheet separating coil I6. Thiscauses the cycle to repeat.

The described circuit is designed for apparatus in which not only thefeed of an entire sheet, but also the partial feed of a sheet, say onlyone foot at a time to a shear press, may be controlled manually. In suchcase a single sheet lift is followed by a whole series of sheet feedmovements to the press. For this purpose the feed roller might be leftenergized continuously, but that is not altogether desirable because ofwaste of energy, and possible overheating of the feed roller. Insteadthe feed roller preferably is energized only during its feed action, andis then reduced in energization to a value sufficient to hold the sheetup against the roller, although not enough to feed the sheet, Inaccordance with the present circuit, instead of the full energizationtaking place strictly in time with the operation of the feed motor, thetime delay circuit I84, I86 prolongs the full energization for a briefinterval, say one-half or one second, to make sure that the sheet doesnot break away from the feed roller because of its own inertia when theroller stops abruptly.

Thus in a simpler form the circuit of Fig. '7 might provide forcontinuous fully automatic feed of sheets, one immediately after theother, with continuous energization of the feed. motor 28 and the feedroller 24. In slightly more complex form the feed roller may bede-energized between feed operations. In still more complex form thefeed motor may be de-energized between feed operations. In still morecomplex form the feed roller may be energized with two degrees ofmagnetization, a lesser one for holding but not feeding a sheet, and astronger one for feeding the sheet. In the present circuit there is thestill further refinement of prolonging the full energization ormagnetization of the roller beyond the rotation of the motor, a featureparticularly useful for partial or incremental sheet feed.

Circuit breaker I I8 is used in this circuit to protect the thyratron II4, and the main coil, and to act as a cut-off device if the tube isoperated at maximum load for too long a time. The circuit breakerincludes a thermal time delay mechanism to take care of the possibilityof a sheet not being raised. It will be recalled that the raising of asheet is what cuts off the energization of the main coil I6, and if nosheet is raised to the trip switch 44 something may be assumed to bewrong, and instead of letting the main coil be subjected to fullenergization indefinitely, it is cut off after, say four seconds, whichis beyond any reasonable time needed to raise a sheet.

Secondary II6 of transformer H2 is the filament heating source forthyratron H4. Transformer secondary 222 of transformer I16 is used toheat the cathode of tube I94. The plate circuit of this tube is supplieddirectly from the line, rather than from a transformer secondary.Secondary 224 of transformer I10 is used to heat the cathode ofthyratron I12. Secondary 226 of transformer I19 is used to supply platecurrent to thyratron I12, and consequently to magnetize the feed roller24.

The rectifier 239 across the main coil I6 is used to give increased lifeto thyratron H4, and incidentally add energy to the main coil I6, Therectifier 230 is faced in direction opposite to the rectifier action ofthe tube, and functions during the negative plate cycle or rectifiercycle of the tube to discharge some of the magnetic energy of the maincoil. It should be kept in mind that we deal here with a heavilyinductive circuit. The rectifier 230 may be termed a back rectifier.

An alternate idea which might be used but is thought less preferable isthe use of a shunt circuit 232, 234 across the thyratron II I, thisbeing a series R. C. circuit of very small current value to just effectthe proper commutation time of the tube. In either case the idea is tohelp lessen the problem caused by tearing of electron surface materialfrom the cathode of the tube because of the interrupted or pulse natureof the operation.

The use of a rectifier 23!! has an important advantage over the use of ashunt circuit and that is in restoring or making useful some energywhich would otherwise be wasted. This is symbolized in Fig. 5 by theparts 232, 234, 236 added to the normal increments I56, I58, I58, theparts 232, 234 and 236 corresponding to the energy fed back from themain coil. This is apart from the improvement in commutation. This sameidea has here been employed also in connection with the feed rollercircuit and even in connection with one of the relay circuits.Specifically the back rectifier- 238 serves the purpose of improvingcommutation of thyratron I12 and at the same time adding energy to thecircuit. The back rectifier 240 is used across the motor circuit to addenergy to the circuit. The back rectifier of tube I94 is indicated at242 and provides additional energy in the non-conducting cycle of tubeI94, the additional energy going to relay I92. In all there are fourback rectifiers used across inductive loads for the same principle aswas explained above, except that in the case of one of them (rectifier248) there is no question of commutation at a cathode, but in all ofthem there is some restoration of current from inductive load.

Resistor 244 is used in the circuit to connect the cathode and screengrid to the plate circuit to aid in grid rectification for the timingcircuit.

In the description of the circuit of Fig. '7 I mentioned the possibilityof only partially instead of wholly collapsing the field of the maininduction coil I6. This may be explained with reference to Fig. 6 of thedrawing, in which it Will be seen that the growth curve or saw-toothwave is much like that shown in Fig. l, except that a minimum currentvalue is provided somewhat above the zero current axis 2%. This is arefinement which may be resorted. to when dealing with sheets which tendto repeatedly adhere together, as, for example, if coated. with a tackyoil film. The partial energization level 253 may be made such to holdthe sheets in slightly fanned or separated condition, so that they willnot re-adhere each time they descend. Thus the growth current causes aprogressive fanning of the sheets until the uppermost sheet reaches thefeed roller, at which time the up=permost sheet is held by the reedroller and the remaining sheets are permitted to descend almost all theway, but not quite far enough to rest firmly on one another with thepossibility of readhering. To accomplish this result it is merelynecessary to so adjust the lowering of the trig ger wave of thethyratron Ht (as determined by the inter-related potentiometer adjust?its 142 and I53) as to provide email, unli'o cly main-- tainedincrements of plate current instead of complete cut-off.

To summarize the operation of the circuit of Fig. 7, thyratron I it actsas a valve to control the main sheet lifting coil Iii. The transformersec ondary I44 supplies plate current and the trans" former secondary13d supp-lies a trigger wave to the grid. The phase of the trigger waveis shit by the phase shifting circuit I32, i3 1. The height of the axisof the t wave determined by adding bias pot. ial supplied from atransformer secondary and bridge rectifier and potentiometer. In thepresent case there are two such bias circuits, one of which Hit, 142)elevates, and the other of which (hit, I33, I60) depresses the triggerwave, the latter being effective when the coil is not functioning, andthe former being effective when it is. The growth of the plate currenttakes place because the trigger wave axis is raised by discharge ofpotential from the decay circuit 152, I54.

Thyratron I12 acts as a valve to control the magnetization of the feedroller 29. Trans former secondary 22d supplies plate current, andtransformer secondary I65 supplies a trigger wave to the grid. The phaseof the trigger wave shifted by phase shifting means Ht, lit. The heightof the axis of the trigger wave is estab lished by bias potentialsupplied. by transformer secondary HEB, rectifier 183 and potentiometerI82. This is adjusted to supply the needed current for the sheet holdingThe magnet-- ization is increased during the sheet feeding stage byraising the trigger wave this being done by sending current throughresistor 208, the current being supplied by relay I92 controlled by athird thyratron ice. The relay I"? also supplies current to operate themotor If it be desired to delay the start of the sheet feeding operationuntil after ample time for collapse of the main field and the fannedsheets, such delay is provided by a time delay circuit associated withtube Hi3 using C. circuit I96, I98. The delay in firing of tube Hi ldelays both rotation and full magnetization of the feed roller.

If it be desired to briefly continue iuil energization of the rollerafter motor stops. in order to compensate for inertia of the movingsheet, such prolongation is provided. by the time delay or decay circuitiitl, llf semiautomatic sheet feed or fractional sheet feed is desired asuitable normally open manual. or

treadle switch -220'is employed, the switch 2H1 being opened oreliminated, but for fully auto matic feed of successive sheets theswitch 213 kept closed.

Three phase electronic circuit Three phase power supply is available inmost industrial plants, and is preferred because it makes more efficientuse of the power available.

A three phase circuit is shown in 8. The main power lines are marked Ll,and L3, with a neutral return N. The three phases are set up in Y form,but the entire circuit may equally well be set up in delta form, withoutthe neu tral return, in those areas of the country where that is thecommon practice. The circuit also can be adapted for two phase powersupply.

Closing pushbutton 300 energizes contactor 302 which remains on throughthe interlock circuit switch 304. The closing of contacts 32 I, 322, 323of the contactor 302 connects the three lines Ll, L2 and L3 to the threetransformers 324, 326 and 328, respectively, and also energizes thetransformer 330. The transformers heat the filaments of the tubes.Contactor 302 sticks by reason of a circuit from Ll through contacts 306through normally closed contacts 308 of a relay 310, through the coil ofcontactor 302, and conductors 312, M4, 316, and thence back to theneutral N of the line. After the tubes have been warmed up switch 332 inseries with line Ll is closed, thereby energizing relay 334 by way ofconductors 336 and 338. This opens the normally closed contacts 340 ofrelay 334, which initiates operation of the three phase circuit shown inthe upper part of the diagram.

This three phase circuit is similar in operation to the previouslydescribed single phase circuit, except that there are three circuits,one for each phase, each of the three circuits being the same as thatpreviously described, but with a single R. C. circuit to control thecurrent growth. The R. C. circuit which lets the trigger wave rise isshown at 342 and 344.

Taking phase 3 or the supply from line L3 as typical, the operation isas follows: Secondary 346 of transformer 328 heats the filament of thethyratron 348. The plate is supplied directly from the line L3 ratherthan from a transformer secondary. Secondary 350 provides the triggerwave, and its phase is shifted by the circuit of condenser 352 andresistor 354. The resistor 353 is used to limit the grid current of. thethyratron 343. The resistor 354 is adjustable to determine the phaseshift. Secondary 358 together with rectifier 360, supplies the phasenumber three portion of the current which provides the posltive o. 0.potential to the grid of the thyratron 343. This positive potential,which is adjustable through potentiometer 352, determines the extent towhich the trigger wave axis is raised. This is the maximum rise of thetrigger wave, when not pulled down to in point, which may be eithercomplete shut-off or a residual value for slight sheet se aration beforeexplained.

The potentiometer 362 which establish blas or height to which thetrigger wave iis ig raised, works in common for all three tubes. Forblas purposes D. C. is wanted, and with a three phase clrcuit the biasproducing current is obtamed from all three phases with three rectifierscombined. In Fig. 7 a full-wave rectifier circuit Was p yed, but in athree phase circuit it is enough to use simple half-wave rectifiers,

itial or rest.

as shown, because :of the overlapping of the three phases.

Secondary 364 of'transf-ornier szs provides .the negative bias used tolower the trigger wave to cut off or reduce the current flowing throughthyratron t lt. Here again there are three secondaries and threerectifiers for the three phases. The potentiometer 368 controls thedegree to which the trigger wave is lowered; andhere again the currentsfrom all three are combined in a single potentiometer to obtain D. C.applied to all three tubes. The bias potential thusobtained is passedthrough the combination capacitor are and rheostat 3 so that whencontacts sec of relay 334 open the potential will decay through thiscombination 342, 34 i, and the time factor of this R. C. circuitdetermines the rate of growth of the current in the plate circuit ofthyratron 348.

Similar description applies to the thyratron 310 of phase 2 and thyrtron 3'52 oi phase I. A fuse 314 is used as a protection in the platecir cult of thyratron 348, and similar fuses are used for the othertubes.

In passing it may be mentioned that while a common control is used toraise the tri ger wave, and a common control is used to lower thetrigger wave, three independent controls are used for the phase shift ofthe trigger'wave at each tube. This is shown at 352, 35$ for thyratronand similar or duplicate controls are shown for thy ratrons 3'59 and312, respectively. This is desir able because each trigger wave must beshifted in phase relative to the plate wave of its own tube, and also tofire alike, because although the tubes come within manufacturersspecification limits they may nevertheless have slight differences infiring potential, and the independent adjustment here provided makes itposs.....e to bring them into uniform operation.

The combined outputs of the three thyratrons is a D. C. power supply forthe main induction coil or sheet separating coil It, and it is a growthcurrent because of increasing increments, all as previously described inconnection with Fig. 5, except that there are increments in threedisplaced phases which are combined in the common main coil It. Thelower terminal of the coil It is connected to the neutral return N, andthe upper terminal has all three cathodes connected to it in common.

The ferrous sheet rises until it reaches the feed roller and trips thetrip switch 3&0, shown at the bottom of the diagram. When trip switch 3%is closed it energizes relay 3B2, thereby open ing contacts 384, and sodeenergizing relay St l and thus permitting contacts S lt to again closewhich provides the negative bias potential necessary to pull the triggerwave down and so collapse the main coil field, because when the fullnegative potential is applied to the trigger wave it cuts off triggeringof the thyratrons (or re duces the output to a small residual).

Besides elimination of the main field, the other things accomplished bythe trip switch are to energize the feed roller and to cause itsrotation. A thyratron tube may be employed to control the supply ofenergy to the feed roller, and preferably dccs so in variable incrementsdetermined by shifting a trigger wave, because in that case thethyratron acts both as a switch and as a current controlling means, withno difficulty of dirtying of contacts, etc. Three phase energization ofthe roller might be employed by using three thyratrons, but in thepresent circuit the 114 apparatus has been simplified by using only asingle phase supply for the feed'roller.

The trip switch 3%, by actuating relay 382, closes contacts 386 and 388.The latter supplies a trigger wave from transformer secondary 392 to thegrid of thyratron 399, tl'irough a phase shift circuit comprising aresistor 3% and capacitor Series resistor 323 is used to limit the gridcurrent. The plate of tube 3% is supplied directly from the line L2,instead of from a secondary. The secondary see of transformer inconjunction with rectifier cs2, provides a positive bias potential toraise the trigger wave. This causes the thyratron to supply current tothe magnetic roller 2%, for a partial or reduced en- .sation for merelyholding but not feeding ti sheet. The rise of the trigger wave axiswhich determines the amount of current flowing through magnetic roller 2is controlled by adjusting a potentiometer set. In this apparatus, as in'7, the feed roller is operated in three the first being zeroenergization during initial lifting of the sheet. second is the presentpartial energisation, sufficient to hold the sheet but not feed thesheet. This is applied the instant the sheet operates the trip switch,and before the roller rotates. The current flowing to the magneticroller is taken from the lines L: and Li, and is controlled by thethy-ratron tube while resistors toe and @538 complete the grid circuit.

With the closing of contacts tilt of relay 382 a time delay circuitcentering .on tube H2 is initiated. This delays action of relay Mil toprovide a delay before starting and putting on the full energization ofthe roller, and among other things, affords time for the sheets, otherthan the top sheet, to descend. Here again grid rectification takesplace through resistor tit and capacitor did, while resistor ii?! limitsthe grid current. The potentiometer y controls to some degree the timeof the delay. The main control is by adjustment of resistor Aid as partof the decay circuit using capacitor ME. The use of a time delay circuitat this point is a refinement, and in many cases will prove neitheressential nor even desirable.

It may be mentioned that in this circuit the action of single relaysimultaneously applies full energization to magnetize the feed rollerand to start the motor which rotates the feed roller. (In thealternative, .it might engage the clutch of a continuously runningmotor.) The primary reason for the time delay is to delay rotation ofthe feed roller, but it then is also advantageous to delay fullenergization because it saves power, and avoids any possibility oftending to feed two sheets forward because of sticking at the back endsof the sheets if the sheets have not been given adequate time to descendfully (or to slightly fanned position). In many installations it will befound that full energization and rotation of the feed roller can bestarted instantly after top sheet reaches the feed roller, but this partof the circuit included in an excess of can to make delay availableshould it be found desirable.

After the time delay of tube ii??? runs out it fires and relay sill isenergized, closing contacts 422. This energizes relay li l throughnormally closed switch or, if the operation. is to be senn-automatic,through a normally open inanual or foot switch 28, in which case switch625 is to be assumed left open or omitted. When relay is energized,contacts 239 close, and provide additional bias potential to the grid ofthyratron 15 3'90, thereby increasing the plate current through themagnetic roller 524. The controlled by a potentiometer the ad itionaposltive bias shunts or bypasses the C. cuit 434, 436, Me.

When relay 42d is energized contacts and 442 also are closed, therebysupplying on) rent to the feed motor (shown symbolically at 28) throughrectifiers 44:3, .3, and rheostat 450. The armature terminals areindicated 452, and the field terminals are iidicated at F? the motorbeing an ordinary shunt motor, wi. 'l advantages previously stated. litreceives the combined rectified current from the three pha e lines Ll,L2 and L3. Rheostat may be to adjust the speed of the motor. The motorreturn goes back through conductors and 345 to the neutral return N.

If a foot switch till; or other manually or ated switch should be usedfeed, a time delay is prefeiz l collapsing the magnetic roller 24. Thisprevent. the sheet from the rolls of the sheet when in root, is hereobtained by the ac which delays the fall of the tr thyratron 398. Thecapacitor resistor 408, tends to absorb applied, thereby slowing up theger wave at the tube as the charge through the R. C. circuit.

When the sheet has been who the trip switch and contacts 338 open,there? ,r timing circuit of tube ill. and relay contacts 422 then opeopens the circuit of relay contacts 438, 440 and 442, which stops thefee motor 28. At the same time contactrelay 424 reopen, which wouldenergize the magnetic roller were same time wholly ole-energized becausecontacts 388 are opened when relay 332 is de-energ ced and cut offentirely the flow of current thr L the thyratron 3st] and the magneticroller.

In addition the de-energization of relay permits contacts 384 tore-close, wh energizes relay 33 1, thereby closing ntacts and openingcontacts 34s. The former a time delay cut-off or non-shect-liit .d ornetio possihle tails of the circuit are next described. One is theprovision of a non sheett safety means to cut off energization of the ncoil event that a sheet is not raised within a reasonable time. in thepresent this is done by the provision of a time delay circuit centeringabout the tube It will be recalled that by closing the operating switch332 the was energized, which in turn opened the contacts S ill toinitiate the growth current, and at the same time closed the contactsliiii. The latter contacts initiate operation of t me delay circuit,which in turn limits total ti ie the growth current circuit may remainin its on condition. This may he, say four seconds, for if a sheet isnot delivered ""ithin some such maximum reasonable time something may beassumed to be wrong, and th power supply to the main coil l 6 is cutoii.

The time delay circuit operates as follows:

Grid rectification takes place through resistor 462 and capacitor Mal,and causes a negative potential to be applied to the grid of tube 568 asa result of the charge built up on capacitor 464. Grid resistor is usedto limit the grid current. Wh n contacts 453 of relay 334 close, thecharge decays through resistors iii-l2 and silt, and when it falls lowenough the tube fires, thereby actuating the relay 3m and opening itscontacts 3%, which shuts 0c the power to the entire system. This is sobecause contacts 308 are in the stick circuit or the main contactor 392,and let the contactor open, which opens contests 32!, and and so opensthe main lines Ll, Lil ant. L l. Resistor t is sod to tie the cathodeinto the plate to aid in g rectification. During all normal operation.sheet is lifted and reaches the roller long before the tube lial fires.The tub fires only if for some reason a sheet does not rise to themagnetic roller.

The foregoing descr n assumed the use of a foot switch lat after lugsemi-automatic and even partial sheet feed, as for example not employedfor partial sheet feed (switch 426 closed) then the sheets are fed oneafter another by reason of the last that when the tail end of the sheetbeing fed leaves the trip switch 380, trip switch opens and so initiatesthe next whole sheet lifting cycle. The growth current or sheet fanningsystem provides some delay anyway, an:- there no need for a special timedelay to insure a between successive sheets. However, a s longer delaywere wanted such a time delay relay could be employed. The til delaycircuit here shown for prolonging the igization oi the feed rollerbeyond its rotation, namel the decay circuit 435, 435, is not neededwhen the foot switch is omitted, and the parts ill-"l, it-ii simply beeliminated. The identical circuit shown with the parts 434, 136eliminated would let the full stage energiration of the feed rollerterminate on termination of rotation.

In this circuit, as in Fig. 7, it is advantageous to employ backrectifiers. The back rectifier 4TB helps commutation in the thyratrons343, 310 and illfi, prolongs their life, and provides a more efficientcircuit, considering that it is heavily inductive. Back rectifier ll?!is used across the relay Sill. Rect er l'lll is a back or con nectedacross the elay 4H3. Rectifier ill is used as the back rect' er forthyratron and feed roller aiding commutation and increasing the circuitefficiency.

Resistor dill is used to tie the cathode of tube 412 to the plate,aiding in grid rectification. Transformer secondary is for heating thecathode of thyratron. 3H secondary is for heating the cathode of tubeuse, and secondary its is for heating the cathode of tube :ll2. In thecase of tubes lilil and M2 the secondaries are connected across thefilaments and across the potentiometers and 129, that is, the filaments,the secondaries and the potentiometers all in shunt re ation.Potentiometer 4% is used to to adjust the range of the time delay causedby the circuit of tube 466, the primary adjustment being th resistor3552.

To summarise the operation of the circuit of 8, thyratrons Mil, and ill.act valves for controlling the field of the main sheet lifting coil it.The lines Ll, L2 and L3 supply plate current. and the three transformersecondaries like secondary 358 supply trigger waves to the grids of thethyratrons. The phase of each trigger wave is shifted relative to itscorresponding plate supply by the three phase shifting circuits like thecircuit 352, 354, these being independently adjustable to establish auniform firing point. The maximum height of the axes of all threetrigger waves is determined by adding positive bias potential suppliedby three transformer secondaries like secondary 2.53 and associatedthree rectifiers like rectifier Iitil, the combined rectified currentsbeing passed through a single potentiometer 382 which affords adjustmentof the height. The trigger wave may be depressed by the addition ofnegative bias potential supplied by three transformer secondaries likethe secondary and three rectifiers like its associated rectifier 3%. Thecombined rectified currents are combined in a single potentiometer 3&3which serves to adjust the drop. The desired growth of the current supplied to the drain coil id is obtained by the use of a decay circuit 332, 3 2 5 which reduces the negative bias taken from potentiometer 368.

The thyratron 3% acts as a valve for controlling the magnetization ofthe feed roller M. Plate current is supplied directly from the line, anda transformer secondary 39?. supplies a trigger wave to the grid. Thephase of the trigger wave is shifted by phase shifting means 3%, 396.The 1 height of the axis of the trigger wave to supply the neededcurrent for the sheet holding stage is established by bias potentialsupplied by a transformer secondary are, rectifier tilt, andpotentiometer Mi l. The magnetization is then increased during the sheetfeeding stage by raising the trigger wave axis, this being done bysending current through bias potentiometer 32. The current to operatethe motor 28 is taken directly from lines Li, L2 and L3 with a neutralreturn N, the three currents being rectified and combined when using aseries motor as here shown. The supply of current to the motor is put onor cut off by a relay 424.

If it be desired to delay the start of the sheet be desired to brieflycontinue full energization r of the roller after the motor stops inorder to compensate for the inertia of the moving sheet, suchprolongation may be provided by the decay circuits 534, 336, 468.

General There may be difiiculty in separating the sheets due to oil filmadhesion. Even when the apparatus is used indoors it often receives astack of sheets fresh from outdoors storage, and because of the coldtemperature in winter, and the long time which it would take for thesheets to acquire room temperature, the sheets stick very tightlybecause the oil film is congealed. A first improvement is to not let thegrowth current come down to zero. Instead the minimum current (as shownin Fig. 6) keeps at least some slight separation of the sheets, and thisprevents them from again adhering and avoids the need to completelybreak the seal each time. An-

18 other step found useful in a serious case is to limit the height ofthe stack to only a few inches so that the separation of the sheets is amaximum during each cycle. Still another step is the retention of aresiduary stack beneath the stack being fed.

It is believed that the construction and operation, as well as theadvantages of my improved apparatus for separating and feeding sheets,will be apparent from the foregoing detailed description thereof.Although single phase power is used for the feed roller, three phasepower may be used. The advantage of the single phase circuit shown iseconomy in construction and apparatus, with some sacrifice in electricalefiiciency. On the other hand, by accepting a greater apparatus cost fora three phase thyratron supply to the feed roller, one may gain slightlybetter electrical efliciency. This is merely a matter of engineeringjudgment for any one particular installation. In general the feed rolleruses much less power than the main induction coil, which explains why inthe present case a three phase supply is used for the main inductioncoil, while using only a single phase supply for the feed roller.Incidentally, there is arguably some ad vantage in single phase supplyfor the feed roller because it may supply a degree of slight pulsationand vibration of the sheet, which may facilitate sheet separation at thelower rear end of the sheet, despite adhesive oil film.

The circuits of Figs. 7 and 8 are almost fully electronic in that evenfor time delay a tube and circuit are employed. An electronic time delayrelay is more trouble-free than an electromechanical time delay relay,but the latter may be used. There is no important change, for nowadaysone can buy a complete electronic time delay relay assembly, just as onecan buy an electro-mechanical time delay relay, to use in a circuit at adesired point.

The sheets may be fed one after another automatically with or withouttime delay therebetween. The sheets may also be fed semi-automatically,requiring a manual or pedal switch operation, and the sheets may be fedincrementally as when working with a shear press or the like. The feedroll may be energized continuously or may be deenergized when not inuse, and if desired, may be energized in two different stages, one forholding and one for feeding. The feed motor may be operated continuouslyor only when in use. When feeding sheets incrementally the fullenergization of the feed roller may be prolonged slightly beyond theoperation of the motor to overcome inertia of the moving sheet. Safetymeans may be provided to guard against prolonged energization of themain coil in the event that no sheet is lifted within a reasonably shorttime. Back rect'ifiers may be provided to increase the efilciency of thecircuit. Re-adhesion of oil film coated sheets may be prevented bymaintaining a small holding current through the main coil instead ofcutting off the current entirely. Many of these features are, of course,optional.

It will be understood that to obtain. the benefit of the growth currentidea it is not at all essential to simultaneously employ the large coilsurrounding the stack, which invention constitutes the subject matter ofmy aforesaid copending application Serial No. 129,662, filed November26, 1949, of which the present application is a continuation-in-part. Inother words, while I have shown my invention applied to a main coilwhich entirely surrounds the stack of sheets, the growth current idea isequally well applicable to numerous other possible forms of magnetemployed. to magnetize the sheets and to thereby cause them to mutuallyrepel.

It will also be understood that while I have shown the sheets disposedand fed horizontally, the sheets and the surrounding apparatus may beoriented differently. For example, the sheets may be stacked in nearlyupright position and repelled at their upper edges, the sheets thenturning away from the group about their lower edges until they engagefeed means.

It will therefore be apparent that while I have shown and described theinvention in several preferred forms, changes may be made in thestructures disclosed without departing from the scope of the inventionas sought to be defined in the following claims. In many claims thereference to a top sheet and the raising of a top sheet to a holdingmeans above the stack, etc. is to be understood primarily in a relativesense, because the sheets need not necessarily be initially stacked inhorizontal position.

I claim:

1. The method of separating the end ferromagnetic sheet from a group offerromagnetic sheets by magnetic repulsion between sheets, whichincludes passing a very feeble magnetic field through the entire groupof sheets and relatively gradually increasing the strength of themagnetic field passing through the entire group of sheets as a functionof time until the end sheet has been moved away a desired distance.

2. The method of separating the top ferromagnetic sheet from a stack offerromagnetic sheets by magnetic repulsion between sheets, whichincludes passing a very feeble magnetic field through the stack ofsheets and relatively gradually increasing the strength of the magneticfield as a function of time until the top sheet has been raised to adesired height, holding the top sheet, then cutting off the magneticfield to permit the remaining sheets to fall, and then removing the heldtop sheet.

3. Apparatus for separating the end ferromagnetic sheet from a group offerromagnetic sheets by magnetic repulsion between sheets, saidapparatus including an electromagnet so positioned as to pass a magneticfield through the entire group of sheets, a source of current toenergize the electromagnet, and means for relatively graduallyincreasing the strength of the current in order to increase the strengthof the magnetic field passing through the entire group of sheets as afunction of time until the end sheet has been moved away a desireddistance.

4. Apparatus for separating the top ferromagnetic sheet from a stack offerromagnetic sheets by magnetic repulsion between sheets, saidapparatus including an electromagnet so positioned as to pass a magneticfield through the stack of sheets, a source of current for energizingsaid electromagnet, a sheet holding means disposed above the stack,means to relatively gradually increase the strength of the current andconsequently the strength of the magnetic field as a function of timeuntil the top sheet has been raised to the sheet holding means, means tosharply reduce the magnetic field to permit sheets other than the topsheet to descend, and means to cause feeding of the held top sheet awayfrom the stack.

5. Apparatus for separating the top ferromagnetic sheet from a stack offerromagnetic sheets, said apparatus including an electroma net sopositioned as to pass a magnetic field through the stack of sheets, asource of current to energize the electromagnet, and means forrelatively gradually increasing the strength of the current in order toincrease the strength of the magnetic field as a function of time untilthe top sheet has been raised to a desired height, said electromagnetcomprising a coil extending entirely around the stack With the axis ofthe coil extending generally in the direction of the plane of thesheets.

6. Apparatus for separating the top ferromagneti sheet from a stack offerromagnetic sheets, said apparatus including an electromagnet sopositioned as to pass a magnetic field through the stack of sheets, asource of current for energizing said electromagnet, a sheet holdingmeans disposed above the stack, means to relatively gradually increasethe strength of the current and consequently the strength of themagnetic field as a function of time until the top sheet has been raisedto the sheet holding means, means to sharply reduce the magnetic fieldto a small amount which permits sheets other than the top sheet todescend but which is adequate to keep the next sheets slightly separatedto prevent ire-adhesion, and means to cause feeding of the held topsheet away from the stack.

7. Apparatus for separating the top ferromagnetic sheet from a stack offerromagnetic sheets, said apparatus including an electroma net sopositioned as to pass a magnetic field through the stack of sheets, asource of current to energize the electromagnet, a thyratron to controlthe flow of current to the electromagnet, and means to apply a triggerwave to the grid of the thyratron in shifting bias or phase relation soas to supply gradually increasing increments of plate current to themagnet in order to increase the strength of the magnetic field as afunction or" time until the top sheet has been raised to desired height.

8. Apparatus for separating the top ferromagnetic sheet from a stack offerromagnetic sheets, said apparatus including an electromagnet sopositioned as to pass a magnetic field through the stack of sheets, asource of current to energize the electromagnet, a sheet holding meansdisposed above the stack, a thyratron to control the flow of current tothe electromagnet, means to apply a trigger wave to the grid of thethyratron in shifting bias or phase relation so as to supply graduallyincreasing increments of plate current to the magnet in order toincrease the strength of the magnetic field as a function of time untilthe top sheet has been raised to the sheet holding means, means toabruptly shift the trigger wave to sharply reduce the magnetic field topermit sheets other than the top sheet to descend, and means to causefeeding of the held top sheet away from the stack.

9. Apparatus for separating the top ferromagnetic sheet from a stack offerromagnetic sheets, said apparatus including an electromagnet sopositioned as to pass a magnetic field through the stack of sheets, asource of current to energize the electromagnet, a sheet holding meansdisposed above the stack, a thyratron to control the flow of current tothe electromagnet, means to apply a trigger wave to the grid of thethyratron in shifting bias or phase relation so as to supply graduallyincreasing increments of plate current to the magnet in order toincrease the strength of the magnetic field as a function of time untilthe top sheet has been raised to the sheet holding means, means toabruptly shift the trigger wave to sharply reduce the magnetic field toa small amount which permits sheets other than the top sheet to descendbut which is adequate to keep the next sheet slightly sep arated toprevent re-adhesion, and means to cause feeding of the held top sheetaway from the stack.

10. Apparatus for separating the top ferromagnetic sheet from a stack offerromagnetic sheets, said apparatus including a main electromagnet sopositioned as to pass a magnetic field through the stack of sheets, asource of current for energizing said electromagnet, means to relativelygradually increase the strength of the currrent and consequently thestrength of the magnetic field as a function of time until the top sheethas been raised to the sheet holding means, an electromagnetic sheetfeed roller disposed above the stack, means to sharply reduce the mainmagnetic field to permit sheets other than the top sheet to descend, athyratron for controlling the supply of current from the source to theroller, means to supply a trigger Wave to fire the thyratron in order tosupply increments of current to the roller, and means to shift thetrigger wave to different bias or phase positions.

11. Apparatus for separating the top ferromagnetic sheet from a stack offerromagnetic sheets, said apparatus including a main electromagnet sopositioned as to pass a magnetic field through the stack of sheets, asource of current for energizing said electromagnetic, means torelatively gradually increase the strength of the current andconsequently the strength of the magnetic field as a function of timeuntil the top sheet has been raised to the sheet holding means, anelectromagnetic sheet feed roller disposed above the stack, means tosharply reduce the main magnetic field to permit sheets other than thetop sheet to descend, a thyratron for controlling the supply of currentfrom the source to the roller, means to supply a trigger wave to firethe thyratron in order to supply increments of current to the roller,and means to shift the trigger Wave to three different bias or phasepositions corresponding to complete cut-off, a holding currentsufficient to hold the top sheet but inadequate to feed the sheet, and afeed current sumcient to grip the sheet tightly for feeding the same.

12. Apparatus for separating the top ferromagnetic sheet from a stack offerromagnetic sheets, said apparatus including a main electro magnet sopositioned as to pass a magnetic field through the stack of sheets, asource of current to energize the electromagnet, an electromagneticsheet feed roller disposed above the stack, a first thyratron to controlthe flow of current to the electromagnet, means to apply a trigger Waveto the grid of the thyratron in shifting bias or phase relation so as tosupply gradually increasing increments of plate current to the magnet inorder to increase the strength of the magnetic field as a function oftime until the top sheet has been raised to the roller, means toabruptly shift the trigger wave to sharply reduce the magnetic field topermit sheets other than the top sheet to descend, a second thyratronfor controlling the supply of current from the source to the roller,means to supply a trigger wave to fire the thyratron to supplyincrements of ourrent to the roller, and means to shift the trigger waveto different bias or phase positions in properly timed relation to theoperation of the main magnet.

13. Apparatus for separating the top ferromagnetic sheet from a stack offerromagnetic sheets, said apparatus including a main electromagnet sopositioned as to pass a magnetic field through the stack of sheets, asource of current to energize the electromagnet, an electromagneticsheet feed roller disposed above the stack, a first thyratron to controlthe flow of current to the electromagnet, means to apply a trigger waveto the grid of the first thyratron in shifting bias or phase relation soas to supply gradually increasing increments of plate current to themagnet in order to increase the strength of the magnetic field as afunction of time until the top sheet has been raised to the roller,means to abruptly shift the trigger Wave to sharply reduce the magneticfield to permit sheets other than the top sheet to descend, a secondthyratron for controlling the supply of current from the source to theroller, means to supply a trigger Wave to fire the second thyratron tosupply increments of current to the roller, and means to shift thetrigger Wave to three different bias or phase positions corresponding tocomplete cut-off, a holding current sufficient to hold the top sheet butinadequate to feed the sheet, and a feed current sufficient to grip thesheet tightly for feeding the same.

14. Apparatus for separating the top ferromagnetic sheet from a stack offerromagnetic sheets, said apparatus including an electromagnet sopositioned as to pass a magnetic field. through the stack of sheets, athree-phase source of current to energize the electromagnet, threethyratrons to control the flow of current to the electromagnet from thethree phases respectively, means to apply trigger Waves to the grids ofthe thyratrons so as to supply increments of plate current to themagnet, and a single means to simultaneously shift the three triggerWaves in order to supply gradually increasing increments in order toincrease the strength of the magnetic field as a function of time untilthe top sheet has been raised to desired height.

15. Apparatus for separating the top ferromagnetic sheet from a stack offerromagnetic sheets, said apparatus including an electromagnet sopositioned as to pass a magnetic field through the stack of sheets, asource of current to energize the electromagnet, means for relativelygradually increasing the strength of the current in order to increasethe strength of the magnetic field as a function of time until the topsheet has been raised to a desired height, and time delay relay means tocut off the supply of current to the electromagnet if a sheet is notraised in response to energization of the magnet.

16. Apparatus for separating the top ferromagnetic sheet from a stack offerromagnetic sheets, said apparatus including an electromagnet sopositioned as to pass a magnetic field through the stack of sheets, asource of current for energizing said electromagnet, a sheet holdingmeans asposed above the stack, means to relatively gradually increasethe strength of the current and consequently the strength of themagnetic field as a function of time until the tcp sheet has been raisedto the sheet hclding means, means to sharply reduce the magnetic fieldto permit sheets 23 other than the top sheet to descend, means to causefeeding of the held top sheet away from the staclz, and a time delayrelay to delay iceding of the top sheet until after the other sheetshave had time to descend.

17. Apparatus for separating and successively feeding ferromagneticsheets from a stack of sheets, said apparatus comprising a support forthe stacl: of sheets, an induction coil extending entirely around thestack of sheets, with the axis of the coil. extending generally in thedirection of the plane of the sheets and generally perpendicular to thedesired direction of separation of the sheets, means to energize thecoil in order to raise and separate the uppermost sheets of the stack,and feed means to receive and feed the uppermost sheet away from thecoil and stack, said means to sue gize the induction coil includingcurrent varying circuit elements arranged and operated to energize theinduction coil with a current of relatively gradually increasingmagnitude in order to help insure the separation of the topmost sheetfrom the immediately suh- J'acent sheet.

18. Apparatus for separating and successively feeding ferromagneticsheets from a stack of sheets, said apparatus comprising a support forthe stack of sheets, an induction coil extending entirely around thestack of sheets, a sheet feeding means disposed near the leading end ofthe stack, drive means for intermittently driving the feed means, meansto energize the induction coil in order to raise and separate theuppermost sheet of the stacl; and to bring it to the feed means, andappropriate switch means for the induction coil interlocked with thedrive means whereby the induction coil is energized while the feed meansis inoperative and is de energized while the feed means is operative,said circuit ele-' ments energize the induction coil including currentvarying circuit elements arranged and operated to energize the inductioncoil with a current of relatively gradually increasing magnitucle inorder to help insure the separation of the topmost sheet from theimmediately subjacent sheet.

19, Apparatus for separating and successively feeding ferromagneticsheets from a stack of sheets, apparatus comprising a support for thestack of sheets, a main induction winding extending entirely around thestack of sheets, a magnetic roller having a magnetizing coil,intermittently operable drive means for intermittently rotating theroller, means to energize the main induction winding in order to raiseand separate the uppermost sheet of the stack and to bring it to theroller, means for supplying current to said coil, means to energize theroller coil to only a limited extent sufficient to hold the uppermostsheet when the feed roller is not rotating, means to more stronglyenergize the coil in order to feed the sheet without appreciableslippage when the roller is rotated, and. appropriate switch means toenergize the main induction winding when the feed roller is stationary,and to de-energize the main induction winding when the feed roller isrotating, said means to energize the main induction winding includingcurrent varying circuit elements arranged and operated to energize themain induction winding by a current of relatively gradually increasingmagnitude in order to help insure the separation of the topmost sheetfrom. the immediately suhjacent sheet.

20. Apparatus for separating and successively feeding ferromagneticsheets from an upright stack of generally horizontal. sheets, saidapparatus comprising a support for the stack. of sheets, an inductioncoil disposed in an u; ght plane and having each of its windingsextending entirely around the stack of sheets, with the top of the coilhigher than the top of the to provide substantial clearancetherehetween, with the aXis of the coil extending generally horizontallyin the direction in which the sheets are to he fed, means to energizethe coil in order to raise and separate the uppermost sheets the saidmeans including current varying circuit elements arranged to supply theinduction co' with a current of relatively gradually iucreas "lgintensity in order to help insure the sep ration of the topmost sheetfrom the irnmedi: y suhiacent sheet, feed means to receive the uppermostsheet when raised and to feed it in a generally horizontal directionfrom the mil and stack.

21. Apparatus for separating and successively feeding ferromagneticsheets upright stack of generally horizontal sheets, said laratuscomprising a support for the stack of sheets, an induction coil disposedin an upright plane and having each of its windings extending Q; elyaround the stack of sheets, with the top of the coil higher than the topof the stack to provide substantial clearance therehetween, and with theaxis of the coil extending generally horizontally in the direction inwhich the sheets are to be fed, means to energize the coil in order toraise and separate the uppermost sheets or the stack, means includingcurrent vary circuit elements arranged to supply the induction coil witha current of relatively gradually increasing intensity in order to helpinsure the separation 01": the topmost sheet from the immediatelysuhjacent sheet, and a magnetic feed roller having a horizontal axisextending across the direction of feed and disposed at a point higherthan the stack hut lower than the top of the induction coil, saidmagnetic feed roller serving to recei e uppermost sheet when raised andto feed it in generally horizontal direction away from. the coil andstack.

22. Apparatus for separating successively feeding ferromagnetic shee sfrom a stack of sheets, said apparatus comprising a support for thestack of sheets, an induction coil extending entirely around the stack.of sheets, with the a; s of the coil extending generally in thedirection of the plane of the sheets and generally perpenclicular to thedesired direction of separation of the sheets, means to energize thecoil in order to raise and separate the uppermost sheets of the stack,and feed means to receive and feed the uppermost sheet away from the cll and stack, means to energize the induction coil including a variableimpedance driven by a motor nd a onerevolution clutch, whereby theinduction coil. is energized by a current of gradually increasingintensity in order to help insure the separation of the topmost sheetfrom the immediately subjacent sheet.

23. Apparatus for separating and successively feeding ferromagneticsheets from a stack of sheets, said apparatus comprising a support forthe stack of sheets, an induction coil extending entirely around thestack of sheets, a sheet feeding means disposed near the leading end ofthe stack, drive means for intermittently driving the feed means, meansto energize the induction coil in order to raise and separate theuppermost sheet of the stack and to bring it to the feed means, andappropriate switch means for the induction coil interlocked with thedrive means whereby the induction coil is energized while the feed meansis inoperative and is de-energized while the feed means is operative,said means to energize the induction coil including a variable impedancedriven by a motor and a one-revo1ution clutch, whereby the inductioncoil is energized by a current of gradually increasing intensity inorder to help insure the separation of the topmost sheet from theimmediately subjacent sheet.

24. Apparatus for separating and successively feeding ferromagneticsheets from a stack of sheets, said apparatus comprising a support forthe stack of sheets, a main induction winding extending entirely aroundthe stack of sheets, a magnetic roller having a magnetizing coil,intermittently operable drive means for intermittently rotating theroller, means to energize the main induction winding in order to raiseand separate the uppermost sheet of the stack and to bring it to theroller, means for supplying current to said coil, means to energize thecoil to only a limited extent sufiicient to hold the uppermost sheetwhen the feed roller is not rotating, means to more strongly energizethe coil in order to feed the sheet Without appreciable slippage whenthe roller is rotated, and appropriate switch means to energize the maininduction winding when the feed roller is stationary, and to de-energizethe main induction winding when the feed roller is rotating, said meansto energize the main induction winding including a variable impedancedriven by a motor and a one-revolution clutch, whereby the maininduction winding is energized by a current of gradually increasingintensity in order to help insure the separation of the topmost sheetfrom the immediately subjacent sheet.

25. Apparatus for separating ferromagnetic sheets from a stack of suchsheets, said apparatus comprising a support for the stack of sheets, aninduction coil extending entirely around the stack of sheets, with theaxis of the coil extending generally in the direction of the plane ofthe sheets and generall perpendicular to the desired direction ofseparation of the sheets, a source of power to energize the coil inorder to raise and separate the uppermost sheets of the stack, andcurrent varying circuit elements between said source and said coilarranged and operated each time a sheet is to be separated to energizethe induction coil with a current of relatively gradually increasingmagnitude in order to help insure the separation of the topmost sheetfrom the immediately subjacent sheet.

26. Apparatus for separating ferromagnetic sheets from a stack of suchsheets, said apparatus comprising a support for the stack of sheets, aninduction coil disposed with the axis of the coil extending generally inthe direction of the plane of the sheets and generally perpendicular tothe desired direction of separation of the sheets, said coil being solarge in diametral dimension that the sheets may be moved through theinduction c the field of the coil runs through the stack, with the stackacting as a core for the field and coil, a source of power to energizethe coil in order to raise and separate the uppermost sheets of thestack, said current varying circuit elements between said source andsaid coil arranged and operated each time a sheet is to be separated toenergize the induction coil with a current of relatively graduallyincreasing magnitude in order to help insure the separation of thetopmost sheet from the immediately subjacent sheet.

27. Apparatus for separating ferromagnetic sheets for removal from anupright stack of generally horizontal sheets, said apparatus comprisinga support for the stack of sheets, an induction coil disposed in anupright plane and having each of its windings extending entirely aroundthe stack of sheets, with the top of the coil higher than the top of thestack to provide substantial clearance therebetween, and with the axisof the coil exending generally horizontally in the direction in whichthe sheets are to be removed and generally perpendicular to the desireddirection of separation of the sheets, a source of power to energize thecoil in order to raise and separate the uppermost sheets of the stack,and current varying circuit elements between said source and said coilarranged and operated each time a sheet is to be separated to energizethe induction coil with a current of relativel gradually increasingmagnitude in order to help insure the separation of the topmost sheetfrom the immediately subjacent sheet.

28. Apparatus for separating ferromagnetic sheets for removal from anupright stack of generally horizontal sheets, said apparatus comprisinga support for the stack of sheets, an induction coil disposed in anupright plane with the top of the coil higher than the top of the stackto provide substantial difference in elevation therebetween, and withthe axis of the coil extending generally horizontally in the directionin which the sheets are to be removed, said coil being so large indiametral dimension that the sheets may be moved through the coil in thedirection of the axis of the coil, and said coil being disposed so closeto the stack that the field of the coil runs through the stack, with thestack acting as a core for the field and the coil, a source of power toenergize the coil in order to raise and separate the uppermost sheets ofthe stack, said current varying circuit elements between said source andsaid coil arranged and operated each time a sheet is to be separated toenergize the induction coil with a current of relatively graduallyincreasing magnitude in order to help insure the separation of thetopmost sheet from the immediately subjacent sheet.

ALEXANDER FOWLER.

References Cited in the file of this patent UNITED STATES PATENTS Number

